This invention relates to a method of heat activating certain top closure panels of a paperboard carton, wherein the interior surfaces of the carton carry a thin layer of polyethylene (PE). This layer or coating serves both to protect the carton contents from direct contact with the paperboard as well as an adhesive when heat activated to cause it to become tacky. Such heat activation is often carried out by hot air jets. The invention exhibits particular utility with respect to cartons of the type shown in U.S. Pat. No. 4,732,275 issued to Hambleton et al, herein incorporated by reference.
A carton of the type of the noted Hambleton patent includes a pair of opposedly facing fin panels which are secured together to form a double thickness fin which is folded, after lamination, down on top of the container, to thereby form a flat topped carton or container. The geometry of the fin forming panels requires heat activation of a specific pattern. The required heat activating pattern for the fin forming panels is that of a sidewise oriented U. While such a pattern can readily be produced by hand, its production by automatic machinery is not known in this art. Accordingly, the use of typical nozzle blocks having small apertures in regular patterns to produce hot air jets such as shown in Egleston U.S. Pat. No. 3,309,841 is not suitable for this particular type of carton. Typical nozzle blocks produce a more or less uniform pattern of hot air jets, to thereby uniformly heat activate the PE coated interior surfaces of top closure panels of paperboard containers.